Shuttle valves for multi-path hydraulic circuits are used to provide fluid pressure from several passages entering the shuttle valve to one passage exiting the shuttle valve. For instance, in 3-way hydraulic circuits in automatic transmissions, shuttle valves are used to supply transmission fluid into a first passage exiting the shuttle valve from either a second or a third passage entering the shuttle valve. The shuttle valve ensures that transmission fluid provided by the second passage is supplied to the first passage without leaking back out through the third passage. Likewise, if fluid is supplied by the third passage, the shuttle valve ensures that this fluid is supplied to the exiting first passage and not back out through the second passage. While shuttle valves employed in this fashion suitably channel fluid into the appropriate passage, several drawbacks exist when this type of valve is used in conjunction with clutch elements on automatic transmissions.
In automatic transmissions, transmission fluid is many times required to be supplied to one clutch element from different sources. As disclosed in U.S. patent application Ser. No. 09/283,567, filed on Apr. 1, 1999, and assigned to the assignee of the present application and hereinafter incorporated by reference, a transmission fluid circuit contains an OD clutch element which is actuated either by a manual shift valve or a electronic solenoid valve. As such, a 3-way shuttle valve can be used to supply transmission fluid pressure from either of these sources to the OD clutch element. This valve ensures that pressure supplied through the OD solenoid valve is provided to the OD clutch element and does not leak back through the manual shift valve. Likewise, the 3-way shuttle valve ensures that fluid pressure supplied from the manual shift valve is supplied to the OD clutch element and does not leak back through the OD solenoid valve.
However, it is important that transmission fluid contained within the OD clutch element is allowed to leak back through the shuttle valve when the OD clutch element ceases to be applied. This leak back ensures that the clutch element is released and does not, instead, burn up due to frictional engagement of rotating elements within the transmission. To provide for this leak back, hydraulic pressure from the OD clutch element pushes the slider valve either toward the passage leading from the manual shift valve or the OD solenoid valve, thereby sealing one of these two passages. The passage remaining open provides the conduit for fluid to leak back from the OD clutch element.
However, if the slider valve is positioned directly under the exiting passage to the OD clutch element, hydraulic force from the clutch element is unable to push the slider valve in either direction. As a result, transmission fluid is trapped in the OD clutch element, thereby maintaining the OD clutch element in an engaged state. The present invention was developed in light of this drawback.